JPS6121826Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to work to reduce residual stress by high-frequency heat treatment of welded parts of austenitic stainless steel pipes in nuclear power plants, and particularly relates to a method of preventing overheating by induction heating around the welded part to be heat treated.

Figure 1 shows an overview of the equipment used to reduce residual stress by high-frequency heating. In this device, a current generated by a high frequency generator 1 is passed through a heating coil 4 wound around the outer surface of a pipe 5 by turning a capacitor 2 and a high frequency transformer. The current flowing through the heating coil 4 generates an induced current on the surface of the pipe 5, thereby heating the pipe. This work mainly involves on-site work at a nuclear power plant, and there are many obstacles near the pipe welds that will be heated. An example is shown in FIG.

If there is a conduit 8 (a steel pipe with a cable running through it) near the piping 5, a part of the magnetic flux generated during induction heating by the heating coil 4 leaks, and this leaked magnetic flux causes the conduit 8 to heat up. and damage the cables inside. Furthermore, power loss due to leakage magnetic flux increases.

From the examples shown above, the shortcomings of the conventional methods are summarized as follows.

b) If there is an obstacle such as a conduit near the heating coil (target welding part), the conduit, etc. may be heated to approximately 100℃ due to leakage magnetic flux from high-frequency induction heating, and the cable inside may be damaged. be. Figure 3 shows an example confirmed in an experiment. According to FIG. 3, when the surface temperature of the pipe 5 (point A) is 550°C, the temperature of the conduit (point B) rises to about 115°C.

(b) Conventionally, in order to prevent heating of the conduit, it was necessary to remove the conduit and the cable.

An object of the present invention is to provide a nuclear power plant having an austenitic stainless steel pipe having a welded part to be heat treated, and a conduit provided in the vicinity of the welded part of the pipe to be heat treated. The purpose of this invention is to prevent the electric conduit from being heated by leakage magnetic flux when performing high-frequency induction heating of the electric conduit.

The feature of the present invention is that the high-frequency power plant used in a nuclear power plant has an austenitic stainless steel pipe having a welded part to be heat treated, and a conduit installed near the welded part of the pipe to be heat treated. The heating equipment includes a heating coil wound around the outer surface of the welded portion of the piping to be heat treated, a high frequency generator, a capacitor and a high frequency transformer for passing a high frequency current through the heating coil, and a vicinity of the heating coil wound around the piping. A copper ring or a copper tape is provided on the outer surface of the electric conduit so as to surround the electric conduit via an air layer or an insulating layer made of an insulating material.

This invention was developed after confirming through experiments that the electric conduit tubes installed in the surrounding area were heated by leakage magnetic flux during high-frequency induction heating, and examining various means to prevent this heating. .

An embodiment of the present invention is shown in FIGS. 4 and 5. Fourth
In the figure, a copper ring 10 is installed outside the conduit 8, and a ground wire 11 is attached to it. When induction heating is performed using this method, when the outer surface temperature of the pipe 5 is about 570°C, the surface temperature of the electric conduit 8 increases only to about 30°C. Note that an insulating layer made of an air layer is formed between the electric conduit 8 and the copper ring 10.

FIG. 5 shows an example in which a copper tape (a thin copper plate shaped into a tape) is used instead of a copper ring. An insulating material 13 is wrapped around the outside of the electric conduit 8, and a copper tape 12 is wrapped around the outside.

In this case as well, the same effects as in the embodiment shown in FIG. 4 can be obtained. An effective way to wind the copper tape is to use a half-lap method.

A sufficient effect can be obtained if the length of the copper ring 10 and the copper tape 12 is 1.0 to 1.5 times the width _L1 of the heating coil 4. Moreover, almost the same effect can be obtained even if the ground wire 11 is not attached.

According to the present invention, an induced current due to leakage magnetic flux generated when high-frequency induction heating is performed on a welded part of an austenitic stainless steel pipe in a nuclear power plant can be caused to flow through the copper ring. It is possible to prevent heating of conduits that are exposed to heat. Therefore, there is no need to remove the electric conduit or the cable when performing high-frequency induction heating of the welded portion of the piping, resulting in an effect that the work can be performed much more efficiently than in the past.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an outline of the high frequency induction heating equipment, Fig. 2 is a diagram showing the heating coil section, Fig. 3 is a plan view of Fig. 2, and Figs. 4 and 5 are diagrams of the present invention. It is a figure of an Example. 1... High frequency generator, 2... Capacitor, 3
...High frequency transformer.

Claims (1)

[Scope of utility model registration request] In a nuclear power plant having an austenitic stainless steel pipe having a welded part to be heat treated, and a conduit provided in the vicinity of the welded part of the pipe to be heat treated, the outer surface of the welded part of the pipe to be heat treated. A heating coil wound around the pipe, a high frequency generator, a capacitor and a high frequency transformer for passing a high frequency current through the heating coil, and an air layer or an insulating material on the outer surface of the electric conduit near the heating coil wound around the pipe. 1. A high-frequency heating equipment comprising: a copper ring or a copper tape provided so as to surround the electrical conduit via an insulating layer.